1. Field of the Invention
The present invention generally relates to a touch sensor mechanism and the manufacturing method thereof, more specifically to a touch sensor mechanism and the manufacturing method thereof applied in a touch display device, in which, a transparent material with higher dielectric constant and mechanic strength is implemented as a cover lens for touching thereon. The thickness of the cover lens can be reduced in order to enhance the signal-to-noise ratio (SNR).
2. The Prior Arts
Well-known technology of capacitive touch device using touch sensors has already been applied in touch electronic devices/products for years. In general, a solution in transitional capacitive touch sensors uses a cover lens with thickness less than 3 mm. In other words, the touch signal sensing is difficult or distorted due to the thick glass and it results in the judgment mistakes of the touch electronic devices/products. Therefore, reducing the thickness of the cover lens is necessary. However, reducing the thickness of the cover lens also reduces the mechanic strength of the touch electronic devices/products.
In general, capacitance is calculated by the formula C=(∈r∈0*A)/d, wherein ∈r is dielectric constant, ∈0 is free space permittivity, A is area of finger and sensor pad overlap, and d is distance between conducting materials. Therefore, the higher of dielectric constant of the cover lens, the higher of finger's touching capacitance CF. As the calculation of formula, the lower the thickness of the cover lens, the higher the finger's touching capacitance CF. Therefore, lower thicknesses and higher mechanic strength of material are required. In the view point of crosstalk noise from a sensor device to another sensor device, the lower thickness is better for reducing the transmitting distance, and the higher dielectric constant of cover lens, the longer distance between the sensor devices, and the lower current of driving circuit are better for preventing the interaction from the electromagnetic field.
In the touch display device, the signal-to-noise ratio (SNR) is measured according to the count value at the output terminal of sensors. For example, when the finger does not touch the sensors, the unpressed average value is μU, and unpressed standard deviation value is σU; when the finger touches the sensors, the pressed average value is μP, and pressed standard deviation value is σP, in general, the signal-to-noise ratio (SNR) is (μU−μP)/σU. According to the touch sensing theory, CTotal=CF+CP, wherein, CTotal is the total capacitance and CP is a sensor parasitic capacitance which is the capacitance of sensor device itself, and CF is capacitance generated by the finger touching, also called finger's touching capacitance. Signal-to-noise ratio (SNR) is related to the ratio of (CTotal−CP)/CP, that is (CF/CP), and signal-to-noise ratio (SNR) is better in a suitable value, such that the sensitivity will not too high or too low. Therefore, the higher tolerance of crosstalk noise is requested in design specification, the finger's touching capacitance CF related to signal-to-noise ratio (SNR) should be higher.
Recently, because Apple Inc. uses projection-typed capacitive touch devices in their products, projection-typed capacitive touch devices become popular due to advantages of simple structure, high reliability, long lifetime, acceptable sensitivity, acceptable precision, acceptable light transmittance, and multi-touch implementation.
However, this touch sensor technology is not perfect. For example, the capacitance of this touch sensor technology is easily influenced by the electromagnetic field effect of the circuit and the effective size of touch panel using this technology is limited to a mid-small size which is equal to or smaller than 17 inches. Larger size (17˜30 inches) of the touch panel using this technology is only in the experiment or test stages. Many companies are developing and improving the technology for increasing the applicable range of projection-typed capacitive touch displays.
Furthermore, the touch sensor technology is developing from one glass solution/touch on lens (OGS/TOL) to on-cell, on-cell/in-cell hybrid and in-cell, and it will increase the distance between sensor and cover lens, and would cause the assembly/attaching gap such that the finger's touching capacitance CF is decreased and the touch sensitivity is reduced. Moreover, the larger size and the higher density of sensor will cause the much serious influence by the electromagnetic effect.
Therefore, it is necessary to develop a touch sensor technology applied in a touch display device, which can eliminate the problems such as reducing the thickness of the cover lens (for example, the thickness lower than 1 mm) without affecting the mechanic strength of touch electronic devices/products due to the higher mechanic strength (for example, the compressive strength higher than 700 MPa) of cover lens; and reducing the thickness of the cover lens which can increase the finger's touching capacitance CF and the signal-to-noise ratio (SNR) related to the ratio CF/CP for real applications in order to eliminate the problem of reducing touch sensitivity by using the cover lens with higher dielectric constant (for example, the dielectric constant higher than 4.5), such that the tolerance of noise caused by crosstalk can be improved by increasing the finger's touching capacitance CF and serious electromagnetic effect due to the large size touch panel of a touch display device can be also eliminated.